Subsea well equipment, such as subsea trees, employs valves that are typically hydraulically or electrically actuated. The valve actuators normally have an overriding mechanism that allows the valve to be opened or closed manually, rather than hydraulically or electrically. The manual actuation occurs in response to rotation of a drive stem or shaft by an external device, such as a remote operated vehicle (ROV). Subsea well equipment may have other shafts that are rotated by an ROV. An ROV is deployed on an umbilical from a surface vessel and controlled from the surface vessel.
Valve actuators have components in their drive train that may fail or be damaged if the torque imposed by the ROV is excessive. Typically, an operator will calibrate the ROV while at the vessel so that it will not impose a torque greater than the maximum capability of the device that it is to rotate. On occasion, personnel may err and set the torque limit for the ROV too high. If that occurs, a possibility exists that the drive train of the subsea device will be damaged. Retrieving the subsea device for repair can be difficult and expensive.